Use of Boost library classes in kdecore?

[David Jarvie]

On Friday 06 July 2007 23:47:05 koos vriezen wrote:
> 2007/7/7, David Jarvie <lists at astrojar.org.uk>:
> > On Friday 06 July 2007 23:07:36 koos vriezen wrote:
> > > 2007/7/7, David Jarvie <lists at astrojar.org.uk>:
> > > > On Friday 06 July 2007 22:42:39 koos vriezen wrote:
> > > > > Btw. how many timeszones are there anyhow?
> > > >
> > > > In an iCalendar file, I would guess that there would typically be
> > > > only a small number. There could be other applications in the future
> > > > which create a much larger number of instances (e.g. of
> > > > KTzfileTimeZone, if historical information was required for system
> > > > time zones).
> > >
> > > Ok, I thought there wouldn't be more than 24 unique ones, which would
> > > make a map more obvious ..
> >
> > There are around 400 time zones in the system time zone database.
>
> Still a candidate for create on demand, always return the same pointer
> to the same timezone and never delete (but then again I have no idea
> how big these are ..)

If somebody is logged in for weeks or months on end, using KOrganizer 
extensively, they could load and reload calendars many times and each time 
create a new set of KTimeZone instances (ICalTimeZone, derived from 
KTimeZone, actually). I think that there needs to be a deletion mechanism for 
unused ICalTimeZone objects in this case, to avoid ever-increasing memory 
usage. Bear in mind that each iCalendar may contain its own time zone 
definitions, which are not guaranteed to be identical to those in other 
iCalendars. So you could end up with far more than 400 time zone instances.

> > > Unless you don't get my point, ie. difference between subclassing
> > > KShared vs. shared_ptr, first is aware of it's shared ptr, second
> > > isn't.
> >
> > I'm still unclear. Both of them are aware that their pointers are to a
> > shared data object. The two classes appear to be similar, except that
> > KSharedPtr is more limited than shared_ptr, and if it were to be used
> > would need to be subclassed to add the necessary facilities which
> > shared_ptr already has.
>
> No the KShared one can use 'this' to pass to functions that want to
> store and reference that object. An object that has its 'this' pointer
> in a shared_ptr can't do that.

To successfully use reference counting, you need to do it as automatically as 
possible. KShared (alias QSharedData) doesn't do it itself - it's done by 
KSharedPtr (or QSharedDataPointer, which provides automatic cloning when 
non-const methods are called, which is not appropriate for KTimeZone). 
shared_ptr in the Boost library does a similar thing to KSharedPtr, but 
provides other necessary functionality as well.

-- 
David Jarvie.
KAlarm author and maintainer.
http://www.astrojar.org.uk/kalarm